Generalized method for assessment of colorectal carcinoma

ABSTRACT

A method is provided for assessing the generalized genetic change which occurs during tumorigenesis. The method relies on measurement of loss of a large number of alleles from the chromosomes of the tumor cells. The alleles are RFLP markers. The role of any of the particular alleles in tumorigenesis need not be known. The amount of allelic loss allows a prognosis to be made regarding tumor metastasis, tumor recurrence, and mortality.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of grantsGM07309 and GM07184 and CA41183, CA47527 and CA35494 from the NationalInstitutes of Health.

BACKGROUND OF THE INVENTION

Previous reports have focused on the loss of particular alleles inparticular cancers. For example, deletions of chromosomal arm 13q areassociated with retinoblastoma. (Cavenee et al., Nature, Vol. 305, p.779 (1983).) In such cases, the deletions are thought to involve tumorsuppressor genes, which while present in the genome, suppressunregulated growth.

In contrast with such examples of particular genes associated withparticular cancers, more general studies using techniques such as flowcytometry and karyotypic analysis have indicated that gross chromosomalabnormalities occur in cancer cells. These include deletions,translocations, and duplications. However, up until now no method hasbeen provided in the art which assesses overall chromosomalabnormalities at the molecular level. There is a need in the art forsuch a method and for molecular means of providing prognoses of tumorrecurrence, tumor metastasis, and mortality.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of assessing theextent of genetic change in neoplastic tissue.

It is another object of the invention to provide a method or assessingthe extent of genetic change in neoplastic tissue which relies neitheron karyotypie analysis nor on analysis of particular genes implicated incarcinogenesis.

It is yet another object of the present invention to provide a method ofassessing the extent of genetic change in neoplastic tissue in which theloss of a set of polymorphic alleles is measured.

It is still another object of the present invention to provide a methodof assessing the genetic change in neoplastic tissue so that a prognosisof a patient can be determined.

It is another object of the invention to provide a kit for assessing theextent of genetic change in neoplastic tissue.

These and other objects of the invention are provided by one or more ofthe embodiments described below. The present invention provides a methodof assessing the extent of genetic change in neoplastic tissues,comprising the steps of:

isolating a first sample of DNA from a neoplastic tissue of a patientand a second sample of DNA from a non-neoplastic tissue of the patient;

testing the first and second DNA samples for the presence of a set ofalleles;

determining a percentage of loss in the first sample relative to thesecond sample of alleles in said set for which the patient isheterozygous, wherein said set has a sufficient number of alleles suchthat the percentage of loss of alleles of said set for which the patientis heterozygous provides a measure of genetic change in the tumor tissuecorrelating with prognosis.

In another embodiment of the invention the presence of a set of allelesis tested by performing Southern hybridization of the DNAs of the firstand second samples with a set of nucleic acid probes which detectrestriction fragment length polymorphisms.

In yet another embodiment of the invention, the presence of a set ofalleles in said first and second DNA samples is tested by amplificationof regions of the DNA of said first and second samples using pairs ofprimers which bracket regions of DNA containing restriction fragmentlength polymorphisms.

In a preferred embodiment of the present invention, the set of alleleswhich are tested for loss comprise at least one allele from each of thenon-acrocentric chromosomal arms of the human genome.

In still another embodiment of the invention a kit is providedcomprising a set of nucleic acid probes for human alleles, said setdetecting a sufficient number of alleles such that the cumulative lossin neoplastic tissue of alleles detected by said set of probes for whichthe patient is heterozygous provides a measure of the extent of geneticchange in the neoplastic tissue, the extent of genetic change beingcorrelated with prognosis, said probes detecting restriction fragmentlength polymorphisms.

In another embodiment of the invention a kit is provided which comprisesa set of single-stranded nucleic acid primer pairs for human DNA. A pairof primers brackets a region containing a restriction fragment lengthpolymorphism. The set of primer pairs contain a sufficient number ofprimer pairs such that the cumulative loss in a neoplastic tissue of apatient of restriction fragment length polymorphism alleles bracketed bysaid set of primer pairs for which the patient is heterozygous providesa measure of genetic change which correlates with prognosis.

The present invention provides the art with a generalized method whichcan be applied to all types of neoplastic tissues which can be isolatedapart from normal, non-neoplastic tissues, to provide a prognosticindicator of the course of the neoplasm. The method does not rely on anyparticular genetic change occurring in any particular disease.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows graphically the frequency of allelic deletions inindividual chromosomal arms as detected by the analysis.

FIG. 2 shows the accumulated allelic losses in individual tumors. Thefractional allelic loss in each tumor is defined as the number ofchromosomal arms on which the allelic loss was observed divided by thenumber of chromosomal arms for which allelic markers were informative(i.e., those in which DNA from the normal tissue exhibited aheterozygous pattern).

FIG. 3 shows an example of allelotypic analysis comparing DNA fromnormal (N) and carcinoma (C) tissues. Panels A, B, C, D, E and Frepresent six different patients, S141, S7, S191, S153, S98, and S175,respectively. The restriction enzyme and radioactive probe used arelisted below each blot.

DETAILED DESCRIPTION OF THE INVENTION

It is a finding of the present invention that allelic loss in tumorcells is remarkably common. One of the alleles of each polymorphicmarker tested was found to be deleted in at least some tumors. Sometumors lost more than half of their parental alleles. Furthermore, ithas been found that the amount of allelic deletions in tumor tissue hasprognostic value for the patient. Regardless of the size and stage ofthe primary tumor which a patient may have, the percentage of allelicdeletions can provide a prediction of tumor recurrence and metastasis,as well as of resulting death. Thus, the determination of the status ofallelic losses in a tumor, called a tumor allelotype, provides amolecular measure for prognosis in patients with cancers.

Although less frequent than deletions, new DNA fragments were found insome tumor tissues which were not present in the corresponding normaltissue. The new fragments contained repeated sequences of the VNTR type(variable number of tandem repeats).

The extent of genetic change which is measured by the method of thepresent invention is a nonspecific measurement which is independent ofparticular genes or loci. Thus a variety of different alleles maycomprise the set for which the present method tests without altering theprognostic value of the test. However, a sufficient number of allelesmust be used such that the cumulative (or percentage) loss of allelesprovides a measure of the extent of genetic change in the neoplastictissue which is correlated with prognosis. A preferred set of allelescomprises alleles on each of the non-acrocentric arms of the set ofhuman chromosomes. (Acrocentric arms are thought to contain mainly thegenes for ribosomal RNA which are repeated multiply in the genome. Therepeated nature of these sequences would make it difficult to detectdeletions of single copies.) Other sets or subsets of alleles may beused so long as they are still able to provide a measure of the extentof genetic change which correlates with prognosis such as that providedby the preferred set of alleles.

Each probe of the present invention defines a restriction fragmentlength polymorphism (RFLP). That is to say that if one were to screen anormal human population for the presence of such an allele, greater than5% of the humans would display a different sized restriction fragmentcorresponding to the allele. A particular type of RFLP probe which canbe used in the present invention are probes for a variable number oftandem repeats (VNTR).

In order to detect allelic loss in humans it is desirable that theallele being tested is present in two different forms in the normaltissue of the patient. Thus the patient would be heterozygous for theparticular allele. This renders analysis of allelic deletion simple andreliable. In general, only a single copy of the two alleles which arepresent in a human are lost upon allelic deletion in tumorigenesis; theexistence of two distinctly sized fragments for each allele renders theobservation of loss of a single allele a qualitative rather than aquantitative measurement. That is to say, in order to score the loss ofa heterozygous allele one looks for absence of a particular sizedfragment. If in the normal tissue the patient were homozygous for theallele, upon loss of a single copy of that allele the restrictionfragment containing the allele would decrease in intensity by about 50%.Total loss is much easier to detect than a 50% loss.

Nucleic acid probes which detect restriction fragment lengthpolymorphisms for most non-acrocentric chromosome arms are availablefrom the American Type Culture Collection, Rockville, Maryland. Theseare described in the NIH Repository of Human DNA Probes and Libraries,published in August, 1988.¹ Methods of obtaining other probes whichdetect restriction fragment length polymorphisms are known in the art.The statistical information provided by using the complete set of probeswhich hybridizes to each of the non-acrocentric arms of the human genomeis useful prognostically. Other subsets of this complete set can be usedwhich also will provide useful prognostic information. Other subsets canbe tested to see if their use leads to measures of the extent of geneticchange which correlates with prognosis, as does the use of the completeset of alleles.

In the ease of colorectal carcinomas the median amount of allelicdeletions found in each tumor is about 20% of those alleles tested. Itwas found that patients with allelic loss higher than the median were ata significantly greater risk of tumor recurrence and death than thosewith allelic loss below the median. The suitability of other sets ofalleles as a prognostic indicator should be tested on a population ofeoloreetal cancer patients to be sure that similar amounts of allelicloss are found in the population, and that the amount of allelic losscan be correlated with tumor recurrence and death.

To find characteristic levels of allelic loss for other types ofcancers, a population of patients having the same type of cancer shouldbe evaluated. Preferably the population will have 50 or more patients init. Although the median amount of allelic loss for a variety of types ofcancers may vary from type to type, the same trend will hold for all.Larger amounts of allelic loss in a particular tumor indicates a higherrisk of tumor recurrence and death, whereas lower amounts of allelicloss indicate a lower risk. Other tumor types for which the method ofthe invention is useful include carcinomas of the lung, colon, breast,bladder, prostate, liver, and stomach.

According to the method of the present invention, two samples of DNA areisolated from each patient. One DNA sample is isolated from neoplastictissue and a second sample is isolated from non-neoplastic tissue. Thenon-neoplastic tissue can be of the same type as the neoplastic tissueor from a different organ source. It is desirable that the neoplastictissue contains primarily neoplastic cells and that normal cells beseparated from the neoplastic tissue. Ways for separating cancerous fromnon-cancerous cells are known in the art and any such means can be used.For example, DNA isolation from paraffin sections and cryostat sectionscan be used, as well as flow cytometry to separate aneuploid cells fromdiploid cells. DNA can also be isolated from tissues preserved inplastic. Separations based on cell size or density may also be used.Once the tissues have been isolated, DNA can be isolated from the tissueusing any means known in the art. The tissue can be minced orhomogenized and then the resulting cells can be lysed using a mixture ofenzyme and detergent as described in Maniatis, Molecular Cloning, alaboratory manual, Cold Spring Harbor Laboratory, 1982. The nucleicacids can be extracted using standard techniques such as phenol andchloroform extraction, and ethanol precipitation.

Testing for the loss of a particular allele can be accomplished by anumber of means which are described below. As alluded to above, it isdesirable that the alleles used in the allelotype loss analysis be thosefor which the patient is heterozygous. This can be determined byexamining the second sample of DNA which is isolated from non-neoplastictissue of the patient and noting the size and number of fragments whichhybridize to a particular nucleic acid probe for an allele for whichthere is restriction fragment length polymorphism. For example, where ahomozygote would have only a single fragment generated by a particularrestriction enzyme which hybridizes to a restriction fragment lengthpolymorphism probe, a heterozygote would have two distinctly sizedfragments which hybridize to the same probe generated by the enzyme.Determination of heterozygosis is well within the skill of the art.

Loss of an allele is determined by comparing the pattern of fragmentscorresponding to the allele in the normal tissue to the neoplastictissue. For example, if a neoplastic tissue has two fragments for aparticular allele and the neoplastic tissue has one fragment, a loss ordeletion is scored. The number of such allelic losses divided by thenumber of alleles for which the patient is heterozygous yields anindicator factor called FAL (fractional allelic loss) or percentage lossof alleles. The FAL has proven to be a significant factor in prognosisof cancer as shown below in Table 3. The FAL provides a predictive indexof metastasis, tumor recurrence, and resulting death.

One means of testing for loss of an allele is by digesting the first andsecond DNA samples of the neoplastic and non-neoplastic tissues,respectively, with a restriction endonuclease. Restriction endonucleasesare well known in the art. Because they cleave DNA at specificsequences, they can be used to form a discrete set of DNA fragments fromeach DNA sample. The restriction fragments of each DNA sample can beseparated by any means known in the art. For example, an electrophoreticgel matrix can be employed, such as agarose or polyacrylamide, toelectrophoretically separate fragments according to physical propertiessuch as size. The restriction fragments can be hybridized to nucleicacid probes which detect restriction fragment length polymorphisms, asdescribed above. Upon hybridization hybrid duplexes are formed whichcomprise at least a single strand of probe and a single strand of thecorresponding restriction fragment. Various hybridization techniques areknown in the art, including both liquid and solid phase techniques. Oneparticularly useful method employs transferring the separated fragmentsfrom an electrophoretic gel matrix to a solid support such as nylon orfilter paper so that the fragments retain the relative orientation whichthey had on the electrophoretic gel matrix. The hybrid duplexes can bedetected by any means known in the art, for example, the hybrid duplexescan be detected by autoradiography if the nucleic acid probes have beenradioactively labeled. Other labeling and detection means are known inthe art and may be used in the practice of the present invention.

An alternative means for testing for the presence of allelic deletionsis by using the technique known in the art as PCR (polymerase chainreaction). According to this method discrete regions of DNA containingrestriction fragment length polymorphisms are amplified. Amplificationis accomplished by annealing, i.e., hybridizing a pair of singlestranded primers, usually comprising DNA, to the DNA of said first andsecond samples from a patient. The primers are annealed to oppositestrands of the DNA so that they prime DNA synthesis in opposite butconvergent directions on a chromosome. The pair of primers bracket aregion of DNA which contains a restriction fragment length polymorphism.That is to say that the primers anneal to DNA which is adjacent to therestriction fragment length polymorphism. Amplification of the regioncontaining the restriction fragment length polymorphism is accomplishedby repeated cycles of DNA synthesis catalyzed by a DNA polymerase.Preferably the DNA polymerase is Taq polymerase which is relatively heatinsensitive. The DNA synthesis requires the components for DNAsynthesis, i.e., each of the four deoxyribonucleotide triphosphates. Inorder to start a new cycle of DNA synthesis the primers must beseparated from the DNA templates, i.e., the DNA of the first and secondsamples; the separation is readily accomplished by heating to above themelting point for duplex DNA. To restart the next cycle of synthesis theprimers and template DNA are re-annealed. After approximately ten cyclesit is desirable to add additional DNA polymerase to the reactionmixture. The product of the amplification is a duplex DNA fragment,bounded by the primers. The PCR technique is described in U.S. Pat. Nos.4,683,195; 4,683,202; and 4,683,194, which are incorporated by referenceherein.

The amplified region of DNA bracketed by the pair of primers can bedetected in a number of ways. For example, the amplified DNA samples canbe separated on an electrophoretic gel matrix and the separated DNA canbe stained with ethidium bromide. These techniques are very well knownin the art. In some cases, cleavage of the amplified DNA samples with arestriction endonuclease which recognizes a polymorphic sequence withinthe amplified region of DNA is required to generate polymorphicfragments. The amplified DNA can be separated on an electrophoretic gelmatrix and subsequently transferred to a solid support (such as nylon orpaper) on which hybridization with a nucleic acid probe can occur. Thenucleic acid probe is one which is homologous with either one of thepair of primers or with the bracketed region of DNA. The nucleic acidprobe can be detected by any means known in the art. Commonly,radioactivity will be used to label the probe and detection will be byautoradiography.

Primers for use in the polymerase chain reaction technique can bedesigned using the probes which detect restriction fragment lengthpolymorphisms. The primers may be ends of the DNA probes or otherportions which when used still are able to bracket the region containingthe RFLP allele. Primers can be tested for their usefulness using DNAwhich is known to contain a restriction fragment length polymorphism.For example, a DNA sample from a normal tissue of a patient which hasbeen shown by a probe to be heterozygous for a particular allele can beused to test out a pair of primers. If the pair of primers, uponamplification of the DNA sample, yields two or more fragments, then theprimers are useful in the method of the present invention.

Kits are also provided by the present invention which contain eithersets of nucleic acid probes or sets of primer pairs or both. The kitscontain sufficient numbers of probes or primers such that the cumulativeloss of a large enough number of alleles can be determined to provide ameasure of extent of change in neoplastic tissues. The measure iscorrelated with prognosis. The nucleic acids in said kits may beprovided in solution or lyophilized form. Preferably, the nucleic acidswill be sterile and devoid of nucleases to maximize shelf-life.

The following examples are not intended to limit the scope of theinvention. They are provided merely to teach concrete and practicalmeans for carrying out the invention.

EXAMPLE 1

This example demonstrates a way in which allelic deletion analysis canbe performed.

DNA from normal (N) and carcinoma (C) tissues of patient S141 (tumor A)was cleaved with restriction endonucleases (TaqI and MspI) and thefragments were separated by electrophoresis and transferred to nylonfilters. The filters were incubated with the indicated radioactiveprobes. Results are shown in FIG. 3A. Sizes of the polymorphicrestriction fragments are shown on the left of each fragment. Withprobes RM7.4 and g3, the larger allele was lost from the tumor; withprobe EFD 64.1, the smaller allele was lost. The sources anddescriptions of the probes are listed below in Example 2.

EXAMPLE 2

This example demonstrates the allelotypic analysis of 56 primarycolorectal carcinomas, and the amount of allelic loss in the tumorpopulation for each chromosomal arm.

DNA was purified from cryostat sections of 56 primary colorectalcarcinomas removed at surgery and compared to the DNA from normalcolonic tissue of the same patients. Probes detecting RFLPs were used todetermine whether one of the two parental alleles detected by each probewas specifically lost in the DNA from the tumor cells. Allnon-acrocentric autosomal arms were studied; the only genes known to bepresent on the acrocentric arms (13p, 14p, 15p, 21p, and 22p) areribosomal. For each of the 39 non-acrocentric chromosomal arms, enoughprobes were used to ensure that the two parental alleles could bedistinguished in the normal tissue of at least 20 patients (i.e., theinformative patients).

The probes used to study the allelotypic deletions are listed below:

Chromosome 1p (36 informative tumors)--Probe YNZ 2: Y. Nakamura et al.,Nucleic Acids Res. 16, 4747 (1988); Chromosome 1q (47 informativetumors)--Probe YNA 13; Y. Nakamura and R. White, Nucleic Acids Res. 16,9369 (1988); Chromosome 2p (27 informative tumors)--Probe EFD 122: E.Fujimoro et al., Nucleic Acids Res. 15, 10078 (1987); Chromosome 2q (45informative tumors)--Probe YNH 24: Y. Nakamura et al., Nucleic AcidsRes. 15, 10073 (1987); Chromosome 3p (25 informative tumors)--Probe EFD145: E. Fujimoro et al., Nucleic Acids Res. 16, 9357 (1988); Chromosome3q (26 informative tumors)--Probe EFD 64.1: Y. Nakamura et al., NucleicAcids Res. in press; Chromosome 4p (23 informative tumors)--Probe YNZ32: Y. Nakamura et al., Nucleic Acids Res. 16, 4186 (1988); Chromosome4q (20 informative tumors)--Probe KT 218: S Humphries et al., Hum Genet68, 148 (1984); Chromosome 5p (31 informative tumors)--Probes JON 35 E-Aand J0209 E-B: J. Overhauser. J. McMahan and J. Wasmuth, Nucleic AcidsRes. 15, 4617 (1987): Chromosome 5q (55 informative tumors)--Probes213-205, TP5E, C11P11, HF12-65, 105-153; M. Leppert et al., Science 238,1411 (1987); Chromosome 6p (32 informative tumors)--Probe YNZ 132: Y.Nakamura et al., Nucleic Acids Res. 16, 5708 (1988); Chromosome 6q (31informative tumors)--Probe JCZ 30: Y. Nakamura et al., Nucleic AcidsRes. 16, 4743 (1988); Chromosome 7p (22 informative tumors)--Probe RM7.4: R. Myers, et al., Nucleic Acids Res. 16, 3591 (1988); Chromosome 7q(51 informative tumors)--Probe g3: Z. Wong, V. Wilson, A. J. Jeffreys,S. L. Thein, Nucleic Acids Res. 14, 4605 (1988); Chromosome 8p (22informative tumors)--Probe NF-L: G. Lacoste-Royal, M. Mathieu, J. P.Julien, S. Gauthier, and D. Gauvreau, Nucleic Acids Res. 16, 4184(1988); Probe SW 50: S. Wood et al., Cytogenet. Cell Genet. 42, 113(1986); Chromosome 8q (26 informative tumors)--Probe MCT 128.2: Y.Nakamura et al., Nucleic Acids Res. 16, 3590 (1988); Chromosome 9p (27informative tumors)--Probe MCT 112: M. Carlson et al., Nucleic AcidsRes. 15, 10614 (1987); Probe HHH 220: M. Hoff et al., Nucleic Acids Res.15, 10606 (1987); Chromosome 9q (39 informative tumors)--Probe EFD126.3: Y. Nakamura et al., Nucleic Acids Res. 15, 10607 (1987);Chromosome 10p (37 informative tumors)--Probe TBQ 7: T. Bragg, Y.Nakamura, C. Jones and R. White, Nucleic Acids Res. in press (1989);Chromosome 10q (37 informative tumors)--Probe EFD 75: Y. Nakamura, E.Fujimoro and R. White, Nucleic Acids Res. in press (1989); Chromosome11p (33 informative tumors)--Probe EJ: C. Shih and R. A. Weinberg, Cell29, 161 (1982); Chromosome 11q (28 informative tumors)--Probe MCT 128.1:M. Carlson et al., Nucleic Acids Res. 16, 378 (1988); Chromosome 12p (39informative tumors)--Probe EFD 33.2: E. Fujimoro, R. Myers, Y. Nakamura,R. White, Nucleic Acids Res. submitted (1988); Chromosome 12q (24informative tumors)--Probe YNH 15: Y. Nakamura et al., Nucleic AcidsRes. 16, 770 (1988); Chromosome 13q (44 informative tumors)--Probe MHZ47: Y. Nakamura et al., Nucleic Acids Res. 16, 3119 (1988); Chromosome14q (50 informative tumors)--Probe CMM 101: Y. Nakamura et al., NucleicAcids Res. 16, 381 (1988); Chromosome 15q (24 informative tumors)--ProbeTHH 55: T. Holm et al., Nucleic Acids Res. 16. 3117 (1988); Chromosome16p (27 informative tumors)--Probe EKDMA2: E. Wolff et al., NucleicAcids Res. 16, 9885 (1988); Chromosome 16q (42 informativetumors)--Probe 79-2-23: L. Burton et al., Hum. Genet. 74, 425 (1986);Chromosome 17p (56 informative tumors)--Probe YNZ 22: Y. Nakamura etal., Nucleic Acids Res. 16, 5707 (1988); Probe YNH 37.3: Y. Nakamura etal., Nucleic Acids Res. 16, 782 (1988); Probe MCT 35.1: M. Carlson etal. Nucleic Acids Res. 16, 700 (1988); Chromosome 17q (44 informativetumors)--Probe Htk9: Murphy, P. D. et al., Nucleic Acids Res. 14, 4381(1986); Probe THH 59: Y. Nakamura et al., Nucleic Acids Res. 16, 3598(1988); Chromosome 18p (27 informative tumors)--Probe B74: F. Morle etal., Cytogenet. Cell Genet. 37 544 (1984); Chromosome 18q (53informative tumors)--Probe OS-4: Nishisho, I. et al., Jpn. J. Hum. Genet32, 1 (1987); Probe OLVIIA8: Delattre, O. et al., Nucleic Acids Res. 15,1343 (1987); Prose OLVII E10: Marlhens, F., et al., Nucleic Acids Res.15, 1348 (1987): Probe HHH64: Yoshioka K., Yoshioka, N. Nakabepu, K.,Sakaki, Y., Nucleic Acids Res. 14, 3147 (1986); Probe ERT 25: Muller, U.et al., Cytogenet. Cell Genet 46, 16 (1987); Chromosome 19p (44informative tumors) Probe JCZ 3.1: Y. Nakamura et al., Nucleic AcidsRes. 16, 1229 (1988)i Chromosome 19q (37 informative tumors)--ProbeRB1-4: C. Juliet. E. Wolff, Y. Nakamura, and R. White, Nucleic AcidsRes. in press (1989); Chromosome 20p (46 informative tumors)--ProbeCMM6: Y. Nakamura et al., Nucleic Acids Res. 16, 5222 (1988); Chromosome20q (22 informative tumors)-- Probe MS1-27: D. Barker, M. Sehafer and R.White, Cell 36, 131 (1984); Chromosome 21q (27 informativetumors)--Probe MCT 15: Y. Nakamura et al., Nucleic Acids Res. 16.9882(1988); Chromosome 22q (41 informative tumors)--Probe EFZ 31: K. Krapehoet al. Nucleic Acids Res. 16, 5221 (1988); Probe AEB2.3: C. M. Rubin etal., Nucleic Acids Res. in pres (1989); Probe EW7.2: T. Bragg, Y.Nakamura, E. Wolff, J.-M. Lalouel and R. White, Nucleic Acids Res. inpress (1989).

Allelic deletions were evaluated with restriction fragment lengthpolymorphism analyses, examples of which are shown in FIG. 3. DNA frompaired normal colonic mucosa and tumor tissues were cleaved with one ofthree enzymes (Taq I Msp I, or HindIII), and evaluated with probes fromeach non-acrocentric chromosomal arm. Only informative tumors, i.e.,those in which DNA from the normal tissue exhibited a heterozygouspattern for one or more allelic markers from the indicated chromosomalarm, were used to determine allelic loss frequencies. An allelic losswas scored if an RFLP fragment present in normal DNA was lost in atleast 80% of The neoplastic cells, as assessed by comparison of theautoradiographs with histologic evaluation of the cryostat sections fromwhich the tumor DNA was purified.

Alleles from each chromosomal arm were lost in at least some tumors (SeeFIG. 1 and Table I). The frequency of allelic loss varied considerably,however, with alleles from two chromosomal arms (17p and 18q) lost fromover 75% of tumors, alleles from nine arms (1q, 4p, 5q, 6p, 6q, 8p, 9q,18p, 22q) lost in 25 to 50% of tumors, and alleles from the remaining 28arms lost in 7-24% of the tumors.

                                      TABLE I                                     __________________________________________________________________________    LOSS OF ALLELES FROM AUTOSOMAL ARMS                                                                                  # INFORMATIVE.sup.d                                                                      % OF TUMORS.sup.e           CHROMOSOME                                                                              MARKER.sup.a MARKER TYPE.sup.b                                                                       ENZYME.sup.c                                                                        TUMORS     WITH ALLELIC                __________________________________________________________________________                                                      LOSS                         1p       YN22         V         T     36         16.2%                        1q       YNA13        V         T     47         25.5%                        2p       EFD122       S         M     27         7.4%                         2q       YNH24        V         M     45         8.9%                         3p       EFD 145      S         T     25         20.0%                        3q       EFD 64.1     V         T     26         15.4%                        4p       YNZ 32       V         T     23         26.1%                        4q       YNZ 218; TBZ 34                                                                            S;S       T;M   20         10.0%                        5p       JON35E-A; JO209E-B                                                                         S;S       M;M   31         6.5%                         5q       213-205; TP5E;                                                                             S;S;      M;T;T;                                                                              55         36.4%                                 C11P11; HF12-65;                                                                           S;S;      M;M                                                    105-153      S                                                       6p       YNZ 132      V         T     32         25.0%                        6q       JCZ 30       V         H     31         32.3%                        7p       RM 7.4       S         M     22         9.1%                         7q       g3           V         T     51         11.8%                        8p       NF-L; SW 50  S;S       T;H   22         50.0%                        8q       MCT 128.2    V         T     26         7.7%                         9p       MCT 112; NHM 220                                                                           S;S       M;T   27         22.2%                        9q       EFD 126.3    V         M     39         25.6%                       10p       TBQ 7        V         M     37         8.1%                        10q       EFD 75       V         T     37         13.5%                       10p       EJ           V         T     33         15.2%                       11q       MCT 128.1    S         M     28         14.3%                       12p       EFD 33.2     S         M     39         7.7%                        12q       YNH 15       S         M     24         16.7%                       13q       MHZ 47       V         T     44         11.4%                       14q       CMM 101      V         M     50         20.0                        15q       THH 55       S         M     24         12.5%                       16p       EKA2         V         M     27         7.4%                        16q       79-2-23      V         T     42         11.9%                       17p       YNZ 22; YNN 37.3;                                                                          V;V;      T;T;M 56         80.4%                                 MCT 35       V                                                      17q       Htk9; THH 59 S;V       T;T   44                                     18p       B74          S         T     27         44.4%                       18q       OS-4; OL VII A8                                                                            S;S       T;M;  53         77.4%                                 OL VII E10; HHH64;                                                                         S;S       M;M;                                                   ERT 25       V         T                                            19p       JCZ 3.1      V         T     44         11.4%                       19q       RB1-4        V         T     37         16.2%                       20p       CMM6         V         T     46         8.7%                        20q       MS1-27       S         M     22         9.1%                        21q       MCT 15       V         M     27         22.2%                       22q       EFZ31; A-EB2.3; EW7.2                                                                      S;S;V     M;T;M 41         29.3%                       __________________________________________________________________________     .sup.a References to the markers are given in EXAMPLE 2                       .sup.b "V" signifies VNTR markers; "S" signifies restriction site             polymorphism markers.                                                         .sup.c M =  MspI; T = Taq 1; H = HindIII                                      .sup.d # of tumors in which one or nore markers for the indicate              chromosomal arm were informative (i.e., DNA from corresponding normal         tissue exhibited a heterozygous pattern).                                     .sup.e Only informative tumors were used to assess this percentage. Losse     were scored positively only if they were clonal, as described in the text                                                                              

There were 127 examples of allelic deletions in which the patient wasinformative (heterozygous) for markers on both the p and q arms of thechromosome containing the deletion. In 65% of these cases, allelic lossoccurred in only one of the two chromoactual arms. The majority of thedeletions observed in this study therefore represented sub-chromosomalevents, such as might be mediated by interstitial deletion, mitoticrecombination, or gene conversion, rather than loss of a wholechromosome.

EXAMPLE 3

This example demonstrates the amount of allelic loss for individualtumors.

We defined fractional allelic loss (FAL) in a tumor as the number ofchromosomal arms on which allelic loss was observed divided by thenumber of chromosome arms for which allelic markers were informative(heterozygous) in the patient's normal cells. The median FAL in the 56tumors studied was 0.20, in other words, alleles were lost from 20% ofthe evaluable chromoactual arms. In 12 tumors, more than a third of theevaluable chromoactual arms had undergone allelic deletion. (See FIG. 2and Table II)

                                      TABLE II                                    __________________________________________________________________________    LOSS OF ALLELES IN INDIVIDUAL TUMORS                                                CHROMOSOMAL ARMS ON WHICH ALLELIC                                                                       # OF ARMS.sup.b                               TUMOR.sup.a                                                                         MARKERS WERE LOST         WITH NO LOSS                                                                           FAL.sup.c                            __________________________________________________________________________    S7    7q,18q,20p                19       13.6                                 S15   5q,17p,18q                17       15.0                                 S16   17p,18q                   19       9.5                                  S20   9q,12q,17p,18q,20q,22q    17       26.1                                 S22   1p,8p,17p,18p,18q         25       16.7                                 S43   1p,1q,3q,4p,5q,11p,13q,14q,17p,18q                                                                      5        66.7                                 S45   10q,15q,17p,18p,18q       24       17.2                                 S50   2p,2q,6p,6q,8p,15q,17p,17q,18q,21q                                                                      20       33.3                                 S51   4p,14q,17p,18q            20       16.6                                 S59   1q,4p,5q,13q,17p,18p,18q,19p,19q                                                                        15       37.5                                 S61   9q,17p,18q                17       15.0                                 S62   17p,21q                   22       8.3                                  S67   1p,5p,5q,11q,17p,18q      23       20.7                                 S74   4p,5q,7q,11p,12q,16p,16q,17p,18q,19q,22q                                                                10       52.4                                 S82   5q                        22       4.3                                  S89   1q                        24       4.0                                  S91   1p,5q,10q,12p,16q,17p,22q 18       28.0                                 S92                             20       0.0                                  S93   1q,5q,6p,6q,10p,15q,17p,17q                                                                             19       29.6                                 S96   5q,9p,16q,17p,22q         21       19.2                                 S98   2q,9q,15q,17p             21       16.0                                 S99   13q,17p,18q               18       14.3                                 S103  14q,17p,18q               20       13.0                                 S104                            24       0.0                                  S106  4p,5q,5p,9p,17p,17q,18p,18q                                                                             14       36.4                                 S108  10q,17p,15q,19q           21       16.0                                 S109  6p,6q,16q,17p,18p         17       22.7                                 S115  5q,14q,17p,17q,18q,21q    18       25.0                                 S119-A                                                                              1q,6p,6q,14q,17p,18p,18q,21q                                                                            14       39.1                                 S119-D                                                                              6q,9q,18q                 20       13.0                                 S122  3p,6p,6q,8p,9p,9q,17p,17q,18q,22q                                                                       19       34.5                                 S123  1q,5q,6p,6q,7p,7q,9q,18q  18       30.8                                 S124  1q,2q,3q,4q,6p,6q,7q,9q,11p,14q,17p,18q,19q                                                             11       54.2                                 S126  3q                        22       4.3                                  S133  3p,5p,5q,6p,6q,11p,17p,17q,20p                                                                          16       36.0                                 S136  1q,3p,16q,17p,18q,19p     23       20.7                                 S140  4q,5q,8p,12q,17p,18q,19q  18       28.0                                 S141-A                                                                              3q,7p,7q,8p,10p,10q,13q,14q,17p,17q,18p,18q,19p,19q,22q                                                 9        62.5                                 S141-8                                                                              8p,9p,10p,11q,14q,17p,18p,18q,22q                                                                       15       37.5                                 S153  1q,7q,8p,17p,18q,22q      20       23.1                                 S154  4p,17p,18q                21       12.5                                 S161  1p,1q,5q,5p,gq,17p,18q,20p,20q                                                                          20       31.0                                 S162  1q,5q,6q,8p,8q,10q,12p,17p,18q,21q,22q                                                                  14       44.0                                 S165  5q,9p,9q,13q,17p          16       23.8                                 S167  3p,9q,14q,17p,18p,18q,21q,22q                                                                           21       27.6                                 S168  1q,5q,17p,18q             22       15.4                                 S170  5q,18q,22q                27       10.0                                 S173                            21       0.0                                  S174  8p,11p,11q,14q,17p,18p,18q                                                                              21       25.0                                 S175  18q,20p                   27       6.9                                  S177  17p,18p,18q               17       15.0                                 S184  17p,18q                   22       8.3                                  S190  1p,3p,9p,9q,12q,17p,18p,18q                                                                             19       29.6                                 S191  2q,5q,17p,19p             21       16.0                                 PS-6  2p,11q,12p,17p,18q        17       22.7                                 PS-12 17p,18p,18q               21       12.5                                 __________________________________________________________________________     .sup.a Two patients (S119 and S141) had two separate tumors.                  .sup.b = # of arms on which DNA from normal tissue demonstrated               heteroxygosity with one or more allelic markers, but both alleles were        retained in tumor DNA.                                                        .sup.c = Fractional Allelic Loss, as defined in the text.                

EXAMPLE 4

This example demonstrates the prognostic value of Fractional AllelicLoss.

The patients were divided into two groups: those with tumors containingless than the median FAL (Group I, FAL less than 0.2) and thosecontaining greater than the median (Group II). Both groups of patientswere followed for a period averaging 38 months. The two groups ofpatients were of similar sex distribution and age, and the average sizeand extent of invasion (Dukes'classification) of their tumors werenearly identical. The prevalence of another genetic alteration (Ras genemutation) that occurs commonly in colorectal tumors was identical in thetwo groups. Despite these similarities, the patients with more deletions(higher FAL) were significantly more likely to develop recurrent diseasethan the other group (p less than 0.01). See Table III. These patientswere also significantly more likely to die with or from their cancer (pless than 0.01).

                                      TABLE III                                   __________________________________________________________________________                               FOLLOW-                                                  FRACTIONAL           UP.sup.c                                                                            TUMOR                                                                              DUKES'.sup.d                                                                        RAS.sup.e                               ALLELIC LOSS                                                                           # OF   AGE  PERIOD                                                                              SIZE CLASS MU-  TUMOR.sup.f                  GROUP.sup.a                                                                         (MEAN)   PATIENTS                                                                             (MEAN)                                                                             (MEAN)                                                                              (MEAN)                                                                             (MEAN)                                                                              TATION                                                                             RECURRENCE                                                                             DEATH.sup.g         __________________________________________________________________________    I     0.11     27     67   38 MTHS                                                                             5.3 cm                                                                             2.3   52%  30%      26%                                       YEARS                                                   II    0.32     25     67   38 MTHS                                                                             5.6 cm                                                                             2.4   52%  68%      64%                                       YEARS                                                   P VALUE               NS   NS    NS   NS    NS   <0.01    <0.01               __________________________________________________________________________     .sup.a Group I patients had tumors with a Fractional Allelic Loss (FAL)       less than the median value (0.2) of the 56 tumors listed in Table 2; Grou     II patients had tumors with an FAL greater than 0.2.                          .sup.b All patients from Table II with a single carcinoma were included.      .sup.c Average followup period in patients who survive is listed. The         average followup period in all patients combined (i.e., those who are         still alive plus those who died) was 31 and 17.5 mths for group I and II      patients, respectively.                                                       .sup.d Dukes' classification scored as 1.0 for Dukes' A tumors (confines      to muscularis propria); 2.0 for Dukes' B tumors (extension through            muscularis propria), and 3.0 for Dukes' C tumors (metastatic to regional      lymph nodes)                                                                  .sup.e RAS gene mutations in this group of tumors were reported               previously.                                                                   .sup.f Distant metastases developed in all except one patient who             developed tumor recurrence.                                                   .sup.g Death with or from carcinoma. An additional 6% and 12% of group I      and II patients, respectively, died without definite evidence of recurren     carcinoma.                                                                    .sup.h Student's T test.                                                      .sup.i Fisher's exact test.                                              

There was also a significant relationship between allelic deletions andclinical course in the subset of patients with less advanced disease atthe time of surgery (Dukes' stage A or B). In 14 such patients with morethan the median FAL, 11 (79%) developed recurrent disease (usuallydistant metastases) post-operatively. Only two of fourteen stage A or Bpatients in the low FAL group had tumor recurrence (p less than 0.001,Fisher's exact test). Thus the measurement of allelic losses might helpto identify patients with an otherwise relatively favorable prognosiswho could benefit from additional therapy.

EXAMPLE 5

This example demonstrates that genetic variations other than deletionsoccur in cancer patients and are detectable by the method of the presentinvention.

In five different instances of allelotype analysis as described above inExample 1, new bands not observed in the DNA from normal tissue werefound in DNA from the corresponding tumor. Each case involved a probefrom a different chromosomal arm, and these five probes were all of theVNTR type (See FIG. 3B-F).

Autoradiographs of Southern blots prepared as described in FIG. 3, panelA, are shown in FIG. 3B-F. For each normal (N)-carcinoma (C) pair, theresults of digestion with two different enzymes are shown, and the probeis indicated. B: Patient S7; C: Patient S191; D: Patient S153; E:Patient S98; F: Patient S175. Sizes of the major polymorphic restrictionfragments are shown on the left of each autoradiograph, and the newfragments in the tumor samples are marked with asterisks.

Areas of tumors containing a high proportion of neoplastic cells wereisolated and 12 micron thick cryostat sections of these areas were usedto prepare DNA. Grossly normal colonic mucosae adjacent to the tumorswere obtained from each patient and used to prepare control (normal)DNA. DNA purification, restriction endonuclease digestion,electrophoresis, Southern transfer, and DNA hybridization were performedas described (Nature, 318; 377 (1985) and Cancer Research, 47; 4806(1987)).

The size of the new bands in an individual tumor was either decreased(in tumors number S98, S153, and S191) or increased (in tumors S7 andS175) by a similar number-of base pairs regardless of the enzyme used).Although the occurrence of VNTR changes in DNA fragments containing VNTRsequences was rare (five alleles altered of 2900 VNTR alleles examined),no rearrangements of fragments without VNTR sequences were observed inour study (3100 alleles were examined with non-VNTR probes).

I claim:
 1. A method for assessing allelic loss in nucleic acids ofcancerous cells as compared to noncancerous cells of an individual humanpatient having colorectal cancer, which fractional allelic loss isprognostic of clinical outcome of said individual patient, comprisingthe steps of:(1) hybridizing a selected set of nucleic acid probes tonucleic acids isolated from colorectal cancer cells or colorectal cancertissue of said individual patient, said nucleic acids having, beendigested with a restriction enzyme, each member of said selected set ofnucleic acid probes being able to hybridize to an allele of a set ofalleles, for which set of alleles a statistical relationship has beenpredetermined, which statistical relationship correlates:(a) losses insaid set of alleles in nucleic acids of cancerous cells or canceroustissue from patients having colorectal cancer with (b) clinical outcomeof said patients; (2) hybridizing the selected set of nucleic acidprobes of step (1) to nucleic acids isolated from non-cancerous cells ornon-cancerous tissue of said individual patient, said nucleic acidshaving been digested with a restriction enzyme,; (3) based ondifferences in hybridization characteristics of said selected set ofnucleic acid probes to the nucleic acids of step (1) compared to thenucleic acids of step (2), determining the number of allelic losses inthe nucleic acids isolated from cancerous cells or cancerous tissue ofsaid individual patent; and (4) determining a fractional allelic lossvalue by dividing the number of allelic losses determined in step (3) bythe number of alleles in the set of alleles probed for which saidindividual patient is heterozygous.
 2. The method of claim 1 which thenucleic acid probes and the isolated nucleic acids are DNA.
 3. Themethod of claim 1 in which the nucleic acid probes hybridize to DNAwhich contains restriction fragment length polymorphisms.
 4. A methodfor assessing fractional allelic loss in nucleic acids of cancerouscells as compared to noncancerous cells of an individual human patienthaving colorectal cancer, which fractional allelic loss is prognostic ofclinical outcome of said individual patient, comprising the steps of:(1)amplifying regions of nucleic acids isolated from colorectal cancercells or colorectal cancer tissue of said individual patient, using aselected set of pairs of nucleic acid primers, each pair of nucleic acidprimers being able to hybridize to nucleic acids which bracket an alleleof a set of alleles, for which set of alleles a statistical relationshiphas been predetermined, which statistical relationship correlates:(a)losses in said set of alleles in nucleic acids of cancerous cells orcancerous tissue from patients having colorectal cancer, with (b)clinical outcome of said patients; (2) amplifying regions of nucleicacids isolated from non-cancerous cells or cancerous tissue of saidindividual patient with the selected set of pairs of primers of step(1); (3) based on differences in regions amplified from the nucleicacids of step (1) compared to regions amplified from the nucleic acidsof step (2), determining the number of allelic losses in the nucleicacids isolated from cancerous cells or cancerous tissue of saidindividual patient; and (4) determining fractional allelic loss bydividing the number of allelic losses determined in step (3) by thenumber of alleles for which said individual patient is heterozygous inthe set of alleles amplified.
 5. The method of claim 4 in which thenucleic acid primers and the isolated nucleic acids are DNA.
 6. Themethod of claim 4 in which the pairs of nucleic acid primers bracketregions of DNA containing restriction fragment length polymorphisms. 7.The method of claim 1 or 4 in which the set of alleles comprises alleleson chromosomal arms selected from the group consisting of 1q, 4p, 5q,6p, 6q, 8p, 9q, 17p, 18p, 18q and 22q.
 8. The method of claim 1 or 4 inwhich the set of alleles comprises alleles on chromosomal arms 17p and18q.
 9. A method for determining a prognosis of an individual humanpatient having colorectal cancer, comprising the steps of:(1) obtaininga fractional allelic loss value for cancerous cells of an individualpatient according to the method of claim 1 or 4; (2) applying to saidfractional allelic loss value of said individual patient a predeterminedstatistical relationship, which statistical relationship correlates (a)fractional allelic loss values of cancerous cells of a population ofpatients having colorectal cancer with (b) clinical outcome; and (3)predicting the clinical outcome of said individual patient.
 10. A methodof selecting a set of alleles for use in colorectal cancer prognosis,comprising the steps of:hybridizing a set of probes or primers able tohybridize to alleles on different human chromosome arms to DNA isolatedfrom cancerous colorectal and noncancerous colorectal tissue of apopulation of patients with colorectal cancer to detect the presence orabsence of the alleles; determining a cumulative percent loss of allelesdetected by the set of probes or primers in cancerous as compared tononcancerous cells for each patient; following each patient of thepopulation to ascertain a clinical outcome of said patient, saidclinical outcome selected from the group consisting of recurrence of thecancer, metastasis, and death due to the cancer; performing astatistical analysis to determine whether a correlation exists betweenthe cumulative percent loss and the clinical outcome, if a correlationexists, the set of alleles is useful for colorectal cancer prognosis.